Generally, the pedal body, as disclosed by the U.S. Pat. No. 2,542,548 and Swiss Pat. No. 279,819, has foot bearing portions at both sides of the axis of the pedal shaft and in parallel thereto.
The front and rear foot bearing portions at the pedal body are spaced at about an interval of a width sufficient to receive the metatarsi of a cyclist's foot only at the phalange side. Therefore, when a cyclist brings the head portions of his metatarsi into contact with the foot bearing portions, the metatarsi at the tarsus side tend to come off the foot bearing portions.
A bony framework at the human foot usually comprises 26 bones in combination, which are divided from an aspect of construction roughly into the tarsi, metatarsi, and phalanges. The tarsi comprise seven bones of the calcaneus, talus, cuboid, navicular, and first through third cuneiforms, in a tight combination. The metatarsi extend forwardly from the tarsi and comprise five first through fifth metatarsi corresponding in number to the toes and arranged laterally. The phalanges extend forwardly in continuation of the metatarsi and comprise 14 bones for the toes, in which a first phalange for the big toe comprises two bones, and other second to fifth metatarsi each comprise three bones for other toes.
The talus bears through the tibia a body weight of a person standing on the foot on the ground and shares it to the metatarsi through the navicular and cuboid and to the calcaneus.
The cyclist, when treading the pedal, transmits a treading force to the pedal body through the tarsi and metatarsi, but not through the calcaneus coming off from the pedal body.
From the aspect of the above human body framework, a cyclist transmits his treading force to the pedal body only through the heads of the metatarsi at the phalange side and smoothly moves his ankle joint to perform a proper pedalling operation. On the contrary, the arched structure by the metatarsi and tarsi bears a larger load, so that the cyclist is easily tired, resulting in that he cannot transmit a larger treading force tirelessly to the pedal body, especially when starting the bicycle or driving it on an upward slope.
As a countermeasure to the above, the conventional pedal body is enlarged in the interval between the front and rear foot bearing portions at both sides of the axis of the pedal shaft. In this instance, the head portions of the metatarsi and and the tarsi, are brought into contact always with both the foot bearing portions, so the treading force cannot be given only from the head portions of the metatarsi at the phalange side. Therefore, although the above problem of the larger treading force during a high load may be solved, another problem will be created in that an unsmooth motion of the ankle leads to an improper pedalling operation for driving the bicycle at high speed.